Uh oh! Engine knocking?

[Utahclaimjumper]

 Jake brakes will activate UNCOMMANDED if the seals (three each) in the solenoids are bad or non-existent. Easy to check by removing the wire to each and unscrew the solenoid.>>>Dan

[Bryan]

Update: we tried messing with the clutch inching the bus forward and backwards, after about 5 minutes, it quit doing it and hasn't done it since. We took it for a spin, no issues. Looking back on the situation, when we started it for 10 minutes and didn't hear the knocking, it wasn't until we moved the bus until the knocking started. That made me thing possibly it could still have something to do with the clutch. What do you think? It's like we got it warmed up and it quit. Does to make sense.

On another note, I've always read that this manual transmission is known to grind when switching gears but it's pretty dramatic, and sometimes hard to get it into hear to start with, sometimes even hard to get out of gear into neutral. Is this normal? Thanks!

[luvrbus]

Isn't that a wet clutch ? it may need oil

[luvrbus]

The Jake will activate with out command when the spring breaks in the solenoid,easy to check push the plate or pin down on the solenoid if it doesn't return the spring is broke   

[opus]

It sure sounded like a few cylinders dropping off, I agree....Jake.

[Bryan]

Ok I will check that. can you tell me where the solenoid is? Thanks!

[georgemci102a2]

How bout trying the old stick to ear method to start with ...George

[luvrbus]

The 4 solenoids are under the valve covers the problem should have been worse if the solenoids or seals are leaking with the higher oil pressure while driving JMO,before you go removing the solenoids you better get the o-rings first those are not easy to come buy with out buying the $$$ kit

It will make it a lot easier on you ordering the 0-rings from DD if you don't mention 8v71 just tell them you want the o-rings for the 760,760A or the 765 heads the 60 series uses the same o-rings and solenoids and you won't get the blank look when asking 

good luck

[RickB]

My jakes have never been functional until the low air pressure switch has turned off. Don't you have to have at least 90 lbs of air to engage the hi idle and the buffer?

RB

[luvrbus]

Jakes are not going to work on fast idle unless something is wrong fwiw

[sledhead]

Last time out my jakes worked fine but my hi / low / off switch on the dash is not working ? any thought's

thanks     dave

[luvrbus]

It probably not getting any juice very seldom does both sides of the hi/lo switch goes out at the same time turn the Jake on you should have power to one side of the buffer switch, that is another thing I don't like about the 2 stage Jakes always electrical problems 1 forty ft wire is better than 4 lol

[bevans6]

Jake heads need only two things to turn on - oil pressure and electricity to the solenoid.  How you control them adds to the complexity.  Most factory installations have a buffer switch that only sends electricity to the solenoids when the master switch on the dash is turned on (and the trans is in gear if automatic or the clutch is out if manual), and the governor (mechanical engine) is at no-fuel.  It's going to no-fuel that extends the push-rod in the buffer switch and engages the micro-switch.  If the engine is at idle or with fuel being applied for power the buffer switch does not engage and the jakes are not allowed to work.  If you have a fast idle buffer switch engaging fast idle uses the same push rod to add idle spring pressure for the faster idle, so by definition the jakes cannot engage.  Fast idle does need air pressure to work, but the jake control in the buffer switch is not affected by air pressure.  If the jakes work but the hi/low/off switch does not turn them off then you have a broken switch, most likely the buffer switch.

If you have a single control jake setup, on/off, then the flow of electricity is from positive in the front electrical bay to the dash on/off master switch, to the clutch/neutral switch, to the buffer switch then to both banks of solenoids.  If you have a Hi/Low/Off setup, the flow of electricity is from the rear engine compartment bus to the solenoid switch, then to the clutch/neutral switch, then to the master switch, then two runs back to the solenoids.  In high both banks are engaged, in low only one bank is engaged.  Since the flow of electricity is to the buffer switch first and then all the rest of the control switches a broken or mis-adjusted buffer switch can be always engaged, and just a gummed up pushrod inside the buffer switch can do that.

If you want to test if the jakes are working, you can warm up the engine, turn the jakes on, rev the engine to 1800 - 2000 rpm and release the speed lever.  You should hear the jakes engage as the engine falls back to idle, then disengage as the engine reaches idle.  While the speed is falling the engine is at no-fuel, then it goes to idle.  The engine might stall as it tries to recover from no fuel to idle with the jakes on.  If you have an automatic with a neutral switch in the control this test won't work unless you bypass that switch so the jakes work in neutral.

[luvrbus]

The Jakes can be wired so many different ways some of these bus people amaze me with all the complex wiring they do for Jakes that is not necessary

[bevans6]

My bus, when I got it, had some funky Jake wiring that didn't work at all.  I pulled it all out and put it back to the stock setup from the MCI manual for single stage on/off jakes using the factory wires.  That worked fine, but the jakes still didn't work - but I couldn't tell because I didn't know what they were supposed to feel like, I just thought the advise that they didn't work all that great in the first place was right so I stopped worrying about it and forgot about them.  Later, when I pulled out the engine to replace it I looked into it further and they were not only adjusted to around 1/8" clearance, the bridge pipes had all backed off so there was no oil pressure to them...  On the new engine and adjusted right they work OK, but I still rarely use them.  I like them in town mostly, or in stop and go traffic.

Brian